This invention pertains to a method and composition for deinking printed wastepaper. More particularly, this invention relates to a method and composition for deinking noncontact-printed wastepaper, particularly xerographic and laser-printed paper, and mixtures of contact and noncontact-printed wastepaper, using an enzyme mixture characterized by a high ratio of xcex2-glucosidase activity to filter paper units (FPU) activity. The present invention also relates to an assay for evaluating enzymes for use in deinking wastepaper based on the ratio of xcex2-glucosidase activity to FPU activity.
Recycling of waste papers and paper products has generated considerable interest in the pulp and paper industry. In response to increasing environmental awareness and regulatory pressure, the paper industry expects to recover and recycle at least 40% of all paper produced in the U.S. by 1995. Proposed regulations require even higher recoveries of certain grades of paper. (Darlington, W. E. (1992) Tappi 1992 Pulp. Conf. Proc., p. 857.) As the demand for recycled fiber content in paper products grows, the need for improved fiber deinking technologies increases accordingly.
Conventional deinking processes require large amounts of expensive, environmentally hazardous chemicals. Current recycling protocols use caustic soda and other chemicals throughout the recycling process. Because these chemicals tend to discolor the pulp, peroxide is typically added to whiten the pulp to the required brightness. These chemicals are eventually washed away in the waste water, causing serious environmental problems. In addition to their high cost and environmental impact, deinking chemicals disintegrate the paper fibers, resulting in lower quality pulp with poor physical properties.
As an alternative to conventional chemical deinking, enzymatic deinking of wastepaper has received increasing attention during the last few years. Several studies have shown that enzymes such as cellulases, hemicellulases, xylanases and lipases effectively deink xe2x80x9ccontactxe2x80x9d printed wastepaper, i.e., papers produced by traditional offset printing using oil-based inks. For example, cellulases have been used to deink old newspaper when used alone or in combination with conventional deinking chemicals. (Fukunaga, N., et al. (Jap. Pat. 0280683); Kao Corp. (Jap. Pat. 59 09,299); Eom, T. J., et al. (1991) Kami Pa Gikyoshi 45(12):1377-82; and Prasad, D. Y., et al. (1992) Prog. Pap. Recycling 1(8):21.) Ow, S. K. and Eom, T. J. (1990) Proc. EUPECA Symp., Barcelona 37:85-94, reports that newspaper can be deinked without conventional deinking chemicals using a cellulase and hemicellulase-containing culture filtrate. Baret, J. L., et al. (PCT Int. Appl. WO 91/14819) reports efficient deinking of wastepaper comprising old newspapers, colored wood-free shavings and magazines using alkaline cellulase together with conventional deinking chemicals. Neo, P., et al. (1986) J. Wood Chem. Tech. 6(2):147, reports that xylanases promote xe2x80x9cenzyme beatingxe2x80x9d during conventional chemical deinking. Finally, incorporation of an alkaline lipase in the conventional alkaline deinking process reportedly improves the brightness and fiber quality of the deinked pulp. (Sugi, T. and Nakamura, J. (Jap. Pat. 03,249,291); and Sharyo, M. and Sakaguchi, H. (Jap. Pat. 02,160,984)).
While the enzymatic deinking of xe2x80x9ccontactxe2x80x9d printed wastepaper has been achieved, relatively little effort has been devoted to the development of alternative methods for deinking xe2x80x9cnoncontactxe2x80x9d printed papers, the principal component of xe2x80x9cmixed office waste.xe2x80x9d Noncontact-printed papers, including xerographic and laser-printed papers, are notoriously difficult to deink by conventional deinking methods. (Vidotti, R. M., et al. (1992) xe2x80x9cComparison of Bench Scale and Pilot Plant Flotation of Photocopied Office Waste Paper,xe2x80x9d 1992 Pulp. Conf. Proc., TAPPI Press, Atlanta, Ga., p. 643-652.) The noncontact inks (toners) used in xerographic and laser printing consist of colored pigments combined with a thermoplastic resin binder, the latter component comprising synthetic polymers such as polyester, styrene-butyl methacrylate or styrene-butadiene copolymers. (Vidotti et al., supra, p. 643.) The polymers become fused together and permanently affixed to the paper during the xe2x80x9cfixingxe2x80x9d stage of the printing process. During repulping, these fused polymers dissolve into thin, flat particles varying in size from a few to several hundred or more microns in diameter. (Vidotti et al., supra.) Because of this broad range of ink particle sizes, dislodged toner particles are not readily separated from the paper fibers. The larger ink particles, ranging in size from about 100 to about 300 xcexcm in diameter, are too massive to be removed using conventional washing or flotation techniques, yet too small to be screened with existing devices. Moreover, their flat, disk-like configuration prevents toner particles from being separated by conventional centrifugal cleaning. Alteration of the size and shape of these dislodged toner particles requires harsh chemical and/or mechanical treatments such as high shear mixing or kneading. (Okada, E. (1991) 1991 Pulp. Conf. Proc., TAPPI Press, Atlanta, Ga., p. 857-864.) However, such actions are not specific, decrease fiber length, and create excessive fines and debris, resulting in reduced fiber strength. Finding efficient, cost effective and innocuous means for deinking toners from xerographic and laser-printed paper represents perhaps the greatest challenge for the pulp and paper industry.
Jeffries, T. W., et al. (1993) Tappi 1993 Recycling Symposium Notes, TAPPI Press, Atlanta, Ga., p. 183, discloses the use of a commercial cellulase to deink homogenous xerographic-printed wastepaper produced from a defined styrene/acrylate toner stock. Jeffries et al. compare the deinking capacity of cellulase (Celluclast(trademark), Novo Nordisk Bioindustrials, Inc., Danbury, Conn.) with standard deinking chemicals using identical steps of high-consistency pulping. The authors report that this particular cellulase used alone was more efficient than chemicals alone or enzymes used in combination with chemical deinking. However, Jeffries et al. note that additional studies are necessary to evaluate the efficiency of enzymatic treatment on heterogenous office wastepaper which contain a mixture of hard-to-remove noncontact toners.
Jeffries, T. W., et al. (1994) Tappi J. 77(4):173-179, compare the deinking efficiency of several commercial cellulases in pilot plant trials. Although the authors could not attribute toner removal to a specific enzymatic activity, they report that xe2x80x9cenzymes with the highest FPU values performed best for deinkingxe2x80x9d whereas the enzyme with the highest cellulase activity (Enzyme C) was among the xe2x80x9cleast effective in removing tonerxe2x80x9d (p. 177). Jeffries et al. further note that efficiency of enzymatic deinking depends on the particular paper source, i.e., whether the paper was acid- or alkaline-sized. This reference thus suggests that the cellulase be selected based on the pH range of the pulped paper stock, and that a high filter paper units (FPU) value may be more important to the efficiency of deinking than cellulase activity per se.
Kim, T. J., et al. (1991) Tappi 1991 Pulp. Conf. Proc., TAPPI Press, Atlanta, Ga., p. 1023-27, purport to provide an enzymatic method for deinking laser-printed computer printout (CPO) paper. [See also Eom, T. J., et al. (Can. Pat. App. 2,032,256).] Kim et al. report a slight improvement in fiber physical properties and a reduction in dirt count by substituting a cellulase for caustic soda during pulping. Although this preliminary report suggests the use of this enzyme to deink laser-printed white ledger paper, the reference provides no evidence that this cellulase (or any other enzyme) could effectively deink heterogenous office wastepaper, i.e., mixed grades and/or colored papers. The reference does not associate deinking with any specific enzyme activity, nor does it provide a basis for evaluating or identifying enzymes for use with a variety of noncontact toners.
Despite the growing pressure to recycle all grades of papers, relatively little attention has been given to the development of methods for recycling difficult-to-deink xerographic and laser-printed papers, the principal component of mixed office waste. Although preliminary reports suggest that noncontact-printed papers can be deinked using enzymes, none teach enzyme preparations optimized specifically for this type of wastepaper. None of the known methods provides a means for removing mixtures of toner inks from various paper sources.
Thus, a need exists for a reliable, versatile and efficient method for deinking all types of wastepaper, especially mixed office wastepaper comprising a blend of hard to deink toners. There is also a need in the art for an enzyme formulation optimized specifically for deinking noncontact printed paper, but which has general applicability to all types of wastepaper. Finally, a need exists for a simple and definitive assay for evaluating the efficiency of enzyme preparations suitable for all types of wastepaper, including heterogenous office wastepaper.
The present invention provides a practical and efficient process for deinking printed wastepaper. This method is effective in deinking all types of wastepaper, including the difficult-to-deink noncontact-printed papers such as xerographic and laser-printed papers, and mixtures of contact and noncontact-printed wastepaper. The present invention is based on the discovery that mixtures of enzymes having a high ratio of xcex2-glucosidase activity to filter paper units (FPU) activity provide surprisingly improved efficiency of deinking. Also surprisingly, surfactant and cations such as calcium ion facilitate flotation when maintained within defined concentration ranges. The methods disclosed herein are surprisingly more efficient than prior art methods and result in higher quality pulp with improved physical properties, higher brightness, better cleanliness (less residual ink content) and improved freeness.
The subject method for deinking toner from wastepaper comprises the steps of pulping the wastepaper to produce a pulp slurry, adjusting the pH to between about 4 and 6 (or, alternatively, to between about 6 and 8), adding suitable deinking enzymes wherein said enzymes are characterized by a high ratio of xcex2-glucosidase activity to FPU activity, continuing the pulping for at least 10 minutes, and separating the toner particles from the pulp.
Another object of this invention is to provide a method for deinking printed wastepaper, including noncontact-printed paper such as xerographic and laser-printed paper, and mixtures of noncontact and contact printed wastepaper such as xerographic, laser-printed paper, newsprint and magazine papers, using a deinking formulation comprising preselected enzymes. This deinking formulation promotes desirable fiber surface modifications, thus providing high quality deinked pulp. The deinking formulation also reduces the size and alters the shape of released ink particles, thus providing significantly improved flotation efficiency.
Yet another object of the present invention is to provide a composition for deinking noncontact-printed paper, and mixtures of noncontact- and contact-printed papers, containing deinking enzymes as the active ingredient, wherein the enzymes are characterized by a high ratio of xcex2-glucosidase activity to FPU activity. The composition promotes desirable fiber surface modifications, reduces and optimizes toner particle size and affects the shape of released toner particles, thus providing high quality deinked pulp. Preferred deinking formulations of the present invention also comprise optimum concentrations of cations and surfactant, thus providing significantly improved flotation efficiency. Compositions further comprising metal ion chelating agents are of particular interest.
The present invention also provides a simple and definitive assay for evaluating the efficiency of enzymes for deinking wastepaper. This method for selecting suitable deinking enzymes comprises the steps of determining the xcex2-glucosidase activity and FPU activity of said enzymes, and calculating the ratio of xcex2-glucosidase activity to FPU activity. Enzymes having a high ratio of xcex2-glucosidase activity to FPU activity have been found to provide surprisingly improved efficiency of deinking. Also surprisingly, an inverse relationship exists between the xcex2-glucosidase:FPU ratio and the enzyme concentration required for effective deinking; the higher the ratio, the lower the required enzyme concentration. Enzymes with xcex2-glucosidase:FPU ratios of at least 100:1 are preferred. However, enzymes with xcex2-glucosidase:FPU ratios of less than 100:1 give satisfactory results when used at higher concentrations.
The present invention thus provides a practical and efficient means for deinking all types of printed wastepaper, including the difficult-to-deink noncontact-printed papers such as xerographic and laser-printed papers. Enzymatic deinking compositions of the present invention, by virtue of their high xcex2-glucosidase:FPU ratios and optimum cation and surfactant concentrations, offer improved efficiency and wider applicability than prior art compositions. Specifically, deinking compositions of the present invention produce smaller, finer ink particles, thus providing surprisingly cleaner deinked pulp. Deinking compositions characterized by a high xcex2-glucosidase:FPU activity ratio are effective with all types of wastepaper, regardless of ink type or paper source, thus eliminating the uncertainty and restrictions of prior art methods. Finally, the present invention provides a simple and definitive means for assessing the efficiency of potential deinking enzymes, thus eliminating the need for actual pulping trials strictly to evaluate efficacy.
Other objects, features and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. All the percentage units used in the document are calculated on a weight/weight basis unless otherwise specified in the text.